Electronically controlling brake devices are known in the art (Brake Handbook, ‘Electronic brake systems’, 1995, ISBN 3-89059-026-8). They are composed of a hydraulic control unit, also referred to as valve block (VB), and an electronic controller (EC). The hydraulic control unit comprises a motor-and-pump assembly and a valve block flanged thereto. During brake control, the motor-and-pump assembly furnishes the pressurized fluid volume required in the pressure build-up phase. The inlet and outlet valves grouped in the valve block permit the modulation of the wheel brake pressures. The brake lines leading to the wheel brakes are connected to the valve block. The valves are connected hydraulically to the valve block by means of bores. Signals of the four wheel speed sensors are sent to the controller.
It is possible to improve brake pressure control by the provision of one or more pressure sensors in the hydraulic lines that lead to the wheel brake cylinders. The pressure sensors are mounted directly on the valve block in prior art devices on which the invention is based. Apart from pressure sensors, the valve block comprises, among others, electromagnetically operable hydraulic valves. Electric coils necessary for the operation of the hydraulic valves are arranged inside the controller. The brake control device is completed in a later assembly step by joining valve block and controller. To this end, valve block and controller are designed as a so-called magnetic plug. In the joining action, the coils slide over the hydraulic valves arranged in the valve block. This action additionally establishes the electrical contacts between the pressure sensors arranged in the valve block and the circuit carrier arranged in the controller by way of spring contacts.
In the prior art device with pressure sensors arranged in the valve block, the electrical components necessary for the electronic conditioning of the measuring signals received at the pressure sensor membrane are either comprised in a pressure sensor modular unit or, in the case of several pressure sensors, comprised in a pressure sensor module. The pressure sensor unit or the pressure sensor module is thus arranged on the valve block and rigidly connected to the valve block after the assembly of the valve block.
From this ensues the disadvantage that normally the entire valve block must be replaced when one pressure sensor fails. A test for the proper functioning of the pressure sensor(s) can only be carried out after the valve block and the controller have been joined. This causes imponderable conditions that can increase manufacturing costs.
DE 197 55 821 A1 discloses a control circuit and a pressure sensor accommodated in a joint housing of an add-on control device, on the bottom side of which a pressure measuring element with a plug-in pipe is arranged. To form a pressure control device, the plug-in pipe extends into a fluid channel of a hydraulic block when the add-on control device is fitted. It is complicated under manufacturing technology aspects that the hydraulic block includes a blind-end bore, an inserting cone, a supporting disc, and a collecting funnel in the area of the fluid channel in order to connect the fluid channel to the plug-in pipe. This condition requires sufficient space for the attachment of the pipe in the hydraulic block in order to establish the connection of the plug-in pipe with the fluid channel. Several pressure sensors with the associated evaluating circuit are grouped on one common carrier, being attached as an independent assembly in the add-on control device. This fact requires much space and additional effort in testing.
An object of the present invention is to design a pressure regulating device of the type referred to hereinabove in such a fashion that the above-mentioned shortcomings are avoided.
For the sensor-type scanning of a hydraulic channel with a pressure transducer, the invention preferably arranges for a structurally separate arrangement of the pressure measuring cell, which may, e.g., comprise a pressure measuring membrane and a passive uncompensated wire strain gauge, and the electronic circuit for the conditioning of the signals of the wire strain gauge in the unit of the electronic controller.
The electrohydraulic pressure regulating device of the invention is comprised of a valve block and an electronic controller to form a monolithic unit. Preferably, the two units are configured as magnetic plugs.
Thus, the invention obviates the need for the otherwise usual integration of an active electronic circuit for the pre-amplification of signals, for signal conditioning and error compensation of the wire strain gauge in the modular unit of the pressure sensor.
In a preferred embodiment of the invention, the electronic components for the signal conditioning for one or more pressure transducers are realized as a part of a larger integrated circuit IC in the controller.
Preferably, the individual signals of all pressure transducers are conditioned in terms of signal technology for conditioning the sensor signals and subsequently sent to an arithmetic unit. In this operation it is expedient, as will be described hereinbelow, that error compensation is not effected within the circuit but within the arithmetic unit.
In another preferred embodiment, the controller incorporates calculation means, especially configured as one or more microcomputers or microcontrollers that permit minimizing the errors of the measuring chain of each individual pressure channel by the electronic evaluation of two functionally separate calculations of correction variables or correction tables. For example, methods for minimizing errors in the treatment of the pressure measuring signals can be performed with the mentioned calculation means. Thus, it is, e.g., possible to determine the deviations of a pressure transducer as a function of pressure and temperature and/or the deviations of the signal conditioning stage associated with the pressure transducer as a function of the signal input voltage and the temperature by way of point measurements and to memorize the result of this determination.
Preferably, the device of the invention is implemented in electrohydraulic brake systems (EHB).
One of the advantages of the invention is that defective pressure sensors can be checked and exchanged at a substantially lower cost due to the arrangement in the electronic controller than would be the case if the pressure sensor were mounted on the valve block.